set ns [new Simulator]

set nf [open out.nam w]
$ns namtrace-all $nf

 set mytrace [open out.tr w]
 $ns trace-all $mytrace

proc finish {} {
	global ns nf mytrace
	$ns flush-trace

	close $nf
	close $mytrace
	exec nam out.nam &

	exit 0
}

set n0 [$ns node]
set n1 [$ns node]

$ns duplex-link $n0 $n1 1Mb 10ms DropTail

set udp0 [new Agent/UDP]
$ns attach-agent $n0 $udp0

set cbr0 [new Application/Traffic/CBR]
#$cbr0 set packetSize_ 500
#$cbr0 set interval_ 0.1
$cbr0 attach-agent $udp0

set null0 [new Agent/Null]
$ns attach-agent $n1 $null0

$ns connect $udp0 $null0

$ns at 0.0 "$cbr0 start"
$ns at 4.9 "$cbr0 stop"

$ns at 5.0 "finish"
$ns run